A New Hybrid Organic–Inorganic Salt: bis (3-Aminopyridinium)Tetrachlorocobaltate(II), Application in the Synthesis of Nanostructured Co 3 O 4 for Hexavalent Chromium Removal

Single crystals of bis (3-aminopyridinium)tetrachlorocobaltate(II) were successfully synthesized and structurally characterized using single crystal X-ray diffraction. This study shows that the structure is built on inorganic anionic and organic cationic subnetworks stabilized by Cl…Cl and antiparallel offset face to face π-π stacking interactions, respectively. The cohesion of the overall packing is ensured by N–H…Cl hydrogen bonds leading to a three dimensional network. Structural geometry optimization and gap energy determination were performed thanks to DFT calculation. Thermal decomposition of the title compound powder, at 450 °C in air atmosphere, leads to nanostructured Co 3 O 4 as confirmed by X-ray powder diffraction. The obtained cobalt oxide was used as adsorbent for the removal of hexavalent chromium ions from aqueous solution. The effect of contact time was investigated and showed an unusual behavior consisting of the existence of two equilibrium plateaus at 11 mg.g −1 and 15 mg.g −1 which were attributed to surface heterogeneity, as elucidated by scanning electron microscopy analysis. As a consequence, the kinetic data were analyzed in steps and fitted using non linear pseudo-first order and non linear pseudo-second order models. A comparative study with other adsorbents demonstrated the potential of the synthesized Co 3 O 4 via thermal decomposition of the title compound for hexavalent chromium ions removal.